Typical automotive internal combustion engines utilize an idle air control system for the control or stabilization of engine speed during idle operation. Such a system may have an electrically operated valve assembly, which modulates the air passing through a conduit, which bridges the throttle plate, contained within a throttle body, of the air intake to the engine. Internal combustion engine idle air control systems typically meter inlet air to the intake manifold of the engine in response to a difference between actual engine speed and a relatively low target engine speed. Change in engine torque load, for example resulting from change in engine driven accessory load, can force engine speed away from the target speed.
Certain engine torque load changes can occur very rapidly. For example, a step change in torque load can occur during certain transient maneuvers. To reject such rapid torque load changes, the idle air control system must be very responsive. To compensate for an engine load change, a corresponding change in engine torque is administered by changing an amount of fuel and air admitted to engine cylinders. The idle air control system provides for a desired time rate of change in intake air. The fuel control system reacts to the time rate of change in intake air to provide a corresponding time rate of change in injected fuel.